[BE] Fix Avro SR for non-TopicNameStrategy subjects

[iliax]

SchemaRegistrySerde checkSchemaExistenceForDeserialize property added

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[Ronserruya]

Hey @iliax , I opened the related issue #3224
I thought about sending a PR but I see you are already on it and can probably fix it better, in the meantime, I fixed both of the problems I talked about locally.

1. Fix for not being to deserialize if the topic doesn't match:
   Change canDeserialize to always return true;
2. Fix for the avro to json printing the record namespace and union types:
   Added this line: encoder.setIncludeNamespace(false); in the avroRecordToJson method

Here's my working .jar if you want to test it

[iliax]

@Ronserruya Thank you for reporting, I created PR to change behavior in glue SR, we will merge it soon.

As for json encoding - unfortunately we can't fix it the way you provided because deserialize, serialize logic and sample messages generation should be in sync. Default JsonDecoder won't be able to serialize json representation withot namesepace info. Please create separate issue for that, we will thing how we can deal with it separately.